As described in Japanese Unexamined Patent Application Publication Nos. 2000-257578 an 2003-286986 a conventional screw compressor that comprises a screw rotor, which has helical grooves, and a gate rotor, which comprises a plurality of teeth that meshes with the helical grooves, is known.
In such a screw compressor, driving a screw rotor with a motor compresses a compression medium, which is sucked from one end of the screw rotor into a casing, in compression chambers, which are formed by the casing, the grooves of the screw rotor, and the teeth of the gate rotor, and, after the teeth of the gate rotor disengage from the grooves, high pressure gas is discharged from the other end side of the screw rotor.